1. Field of the Invention
The present invention relates to a device for detecting the presence or absence (presence/absence) of liquid such as ink and, more particularly, to a device suitable for detecting the presence/absence of ink held within an ink cartridge mounted in an ink-jet printing device for discharging droplets of ink through a nozzle to thereby effect printing on a medium to be recorded.
2. Description of the Related Art
It has been known to detect the presence/absence of liquid such as ink by a detecting device shown in FIG. 17a. This detecting device comprises a pair of electrodes 92 and 93 provided within an ink cartridge 91 in an opposing relationship, a signal generating circuit 90 for applying a signal A in a pulse or digital form to the electrodes 92 and 93, a resistor R electrically connected between the signal generating circuit 90 and the electrode 92, an A/D converter circuit 94 for receiving a signal B developed between the resistor R and the electrode 92. The voltage amplitude of this signal B varies with a resistance of ink between the electrodes 92 and 93 and is converted into a digital signal C by the A/D converter circuit 94. A CPU 95 receives the digital signal C from the A/D converter circuit 94 therein and detects the presence/absence of ink based on the input digital signal C.
When the signal A is generated from the signal generating circuit 90, the signal B whose voltage is lower than that of the signal A is developed between the resistor R and the electrode 92 due to the ink resistance between the electrodes 92 and 93 as long as the ink exists within the ink cartridge 91, as shown at the left side in FIG. 17b. This voltage magnitude of signal B is converted into the digital signal C ("0" or low level) as shown by C in FIG. 17b and the CPU 95 determines the existence of ink in response to this digital signal C (low value). When no ink is held within the ink cartridge 91, the signal B comes to have the same voltage magnitude as that of the signal A as shown by A at the right side in FIG. 17b. This signal B is converted into the digital signal C ("1" or high level) by the A/D converter circuit 94 as shown by C at the right side in FIG. 17b. The CPU 95 determines the absence of ink in response to this digital signal C (high value). Thus, the CPU 95 detects the presence/absence of ink based on whether the input digital signal C has a high value or a low value.
However, the conventional detecting device requires that the signal B whose voltage level varies according to the presence/absence of ink is converted into the corresponding digital signal C by the A/D converter circuit 94.
As a result, since the detecting device becomes complex in circuit configuration as long as the A/D converter circuit 94 is included therein, it is more likely that the occurrence of its failure increases, thus degrading the reliability of detection of the presence/absence of ink.